1. Field of the Invention
The present invention relates to a shutter for a camera.
2. Description of the Related Art
Although a shutter for a camera is available in various styles and types, as one type there is a shutter for a camera which operates such that an aperture of a lens is closed by closing a plurality of sheets of sectors and a hole for exposure is opened at a central portion thereof by pivoting the sectors. According to opening and closing operation of the sectors, a base portion of each of the sectors is pivotably supported, a drive pin of a sector drive lever is engaged with a drive hole portion provided at a position apart from the support point by a predetermined distance and the sector can be opened by pivoting the lever and can return to an original position by spring force.
FIG. 11 shows the principle of a shutter drive apparatus for operating two sheets of sectors to open and close according to a conventional technology and an outline of a constitution of the shutter drive apparatus is as follows.
Two sheets of sectors 83 are attached between a shutter base plate 81 and a rear plate 82 to thereby enable to open and close lens apertures 81a and 82a. The shutter base plate 81 and the rear plate 82 can be fixed to be apart from each other at an interval capable of installing the sectors pivotably by screws 84.
Respective elements of the shutter drive apparatus are provided on a front face (upper face of FIG. 11) of the shutter base plate 81. First, a sector drive lever 85 formed with projected portions on both sides of a plate-like member formed substantially in a heart-like shape, is provided at a vicinity of a central portion of the upper face of the shutter base plate 81. According to the sector drive lever 85, a bearing portion 85a provided to project at a pivotal center portion thereof is fitted to a support shaft portion 81b provided to project from the upper face of the shutter base plate 81. A sector drive pin 85b is provided straight down from a vicinity of a top portion of a lower face of the sector drive lever 85 and the pin passes through an arc groove portion 81c formed in the shutter base plate and is engaged with an oval groove portion 83a of the sector. Further, respective sectors constituting the shutter 83 are pivotably supported by pivotal center holes 83b and support pins 81d provided to project from a rear face of the shutter base plate. The respective support pins 81d stably support respectively the sector 83 by being engaged with through holes 82b provided at the rear plate 82.
The sector drive lever 85 is biased in the counterclockwise direction by a spring 86, and thereby, the shutter 83 is biased in a direction of closing the shutter 83. A drive coil 87 constituted by winding a coil in a spiral shape and solidifying the coil in a doughnut-like shape, is fixedly attached to a rear face of an ear portion 85c formed on a side of the sector drive lever 85 opposed to a position attached with the spring 86. One lead wire 87a of the coil 87 is connected to an outer peripheral portion of the coil and the other lead wire 87b is connected to an inner peripheral portion thereof. When electricity is conducted from a drive circuit 88 to the coil 87, there is produced magnetic flux an upper side of which constitutes an S pole and a lower side of which constitutes an N pole, for example. Conduction of electricity to the coil 87 can be controlled by the drive circuit 88 to thereby enable to arbitrarily open and close the shutter.
The drive coil 87 is also pivoted centering on the support shaft portion 81b by pivoting the sector drive lever 85 and a pair of permanent magnets 89 and 90 in a shape of a thin plate are provided on a pivotal locus of the center of the coil. These permanent magnets are fixedly attached onto the upper face of the shutter base plate 81 and the one magnet 89 is disposed on a forward side of the pivotal locus of the coil 87 in the clockwise direction at an initial position and is pasted such that an upper face thereof constitutes an N pole. In contrast thereto, the other permanent magnet 90 is disposed on a rearward side of the pivotal locus and is pasted such that an upper face thereof constitutes an S pole.
Since the constitution is constructed in this way, when magnetic force with the S pole on a downward side is produced in the coil by conducting controlled electricity from the drive circuit 88 to the coil 87, by the operation of the magnetic force, a suction force is operated between the drive coil 87 and the magnet 89 on the front side and a repulsion force is operated between the drive coil 87 and the magnet 90 on the rear side to thereby move the drive coil 87 in the clockwise direction and pivot the sector drive lever 85 in the same direction. Thereby, the sector 83 is opened and an exposable state is brought about. Next, when electricity is made to stop conducting to the drive coil 87, the magnetic force is extinguished, and therefore, the sector drive lever 85 returns to the original position by a spring 86 and the shutter is closed.
According to the shutter drive apparatus of the conventional example, the sector drive lever 85 and the drive coil 87 are disposed on different planes and accordingly, there poses a problem in which areas on the planes become large. Further, in addition thereto, the sector drive lever 85, the drive coil 87 and the permanent magnets 89 and 90 are provided at respectively different heights and accordingly, there poses a problem in which a thickness of the shutter becomes large by that amount. Furthermore, the sector drive lever 85 is pivoted by pivoting the drive coil 87 per se and accordingly, there poses a problem in which large kinetic energy is needed and accordingly, power consumption is increased.
In order to resolve the above-described problems, according to a shutter for a camera of the invention, a fixed printed board in correspondence with the shutter base plate in the conventional technology and a movable printed board in correspondence with the sector drive lever in the conventional technology, are provided respectively with an optical axis as a reference, a plurality of coil patterns in a spiral shape are arranged at each of the printed boards and a plurality of sectors are made openable and closable by using electromagnetic force produced by conducting electricity to the plurality of coil patterns to thereby realize small-sized formation and high function formation of the shutter.
According to the shutter of the invention, the respective printed boards and a sector ring are constructed so as to be laminated centering on the optical axis and accordingly, areas of the shutter are reduced while the drive coil occupying a large space in the conventional technology is replaced by the coil patterns and accordingly, the shutter can be thinned also in view of a thickness thereof to thereby promote downsizing of the shutter.
When current controlled by a drive circuit is flowed to the coil patterns arranged on the fixed printed board, depending on a way of winding the coil patterns in the spiral shape, electromagnetic force of an N pole or an S pole is produced respectively on a fixed printed board face and a movable printed board face opposed to each other.
When polarities of both are constituted by a same polarity in directions opposed to each other and initial positions of the coil patterns of the movable printed board are set at positions apart from positions of the fixed printed board and shifted in an advancing direction by a predetermined angle, electromagnetic forces by the two coil pattern produced by conducting electricity from the drive circuit repel each other to pivot the movable printed board in a direction of opening the sectors. When electricity is made to stop conducting to the coil patterns by the drive circuit, the electromagnetic forces of the two printed boards are extinguished, and accordingly, the sector drive lever returns to an original position by a biasing force of a spring and the shutter is closed.
Further, since the coil patterns are formed in the spiral shape, the respective coil patterns can be connected to each other by installing connecting portions of the coil patterns to detour on other faces where connection portions of patterns are not opposed to each other by utilizing through holes perforated in the printed boards such that electricity is conducted to inner end portions thereof.
With regard to drive force in closing the sectors, by controlling a direction of conducting electricity to the coil patterns on either of the printed boards by the drive circuit, a time period of closing the sectors can also be shortened by utilizing, in addition to the biasing force of the spring, attractive force produced by making polarities on the opposed faces different from each other.
Further, according to other means, by arranging a spiral pattern in the same way of winding in view from the same direction to both of the printed boards as the coil patterns of the respective printed boards, there can be produced electromagnetic force having an intensity twice as much as that in the case in which the spiral patterns are arranged only on faces thereof on one side.
Further, according to other means, by alternately arranging spirals of the respective coil patterns in ways of winding in directions reverse to each other, the drive force is increased by simultaneously effecting repulsion and attraction operation.
Further, according to other means, in place of the above-described coil pattern of the fixed printed board, permanent magnets are arranged and the movable printed board is made pivotable by magnetic force of the permanent magnets and by electromagnetic forces produced the coil patterns of the movable printed board. Although the thickness of the shutter is increased by an amount of the thickness of the permanent magnet, strong magnetic force is provided and accordingly, the sectors can be opened by large drive force. When the permanent magnets are arranged in this way, basically, a surface of any one of the permanent magnets is constituted by the same polarity. In contrast thereto, when the coil patterns of the movable printed board are arranged to constitute polarities alternately different from each other, the coil patterns in correspondence thereto are arranged such that polarities thereof differ from each other. Further, also in the case of arranging the permanent magnets in place of the fixed printed board, drive force by strong electromagnetic force can be provided by arranging the coil patterns on two faces of the movable printed board.